Material deposition on large substrates or multiple substrates held by a large holder is widely used in window glass coating, flat panel display manufacturing, coating of flexible films, hard disk coating, industrial surface coating, semiconductor wafer processing, and other applications. In such a deposition system, the magnetron source, the target, and the substrate can be transported relative to each other. At least one dimension of a target needs to be larger than a dimension of the substrate such that the substrate can be fully covered by the material sputtered off the target.
Different designs exist in the conventional deposition systems for large substrates. But the designs all have different drawbacks. In the first example, as shown in FIGS. 1A-1D, a deposition system 100 includes a long narrow rectangular target 110 over a large substrate 115 in a vacuum chamber 120. A magnetron 130 is held behind the target 110. The substrate 115 can be transported in the direction 150 relative to the target 110 and the magnetron 130 to receive a uniform deposition across the top surface of the substrate 115. The magnetron 130 is stationary relative to the target 110. The deposition system 100 can also includes a power supply 140 that can produce an electric bias between the target and walls of the vacuum chamber 120.
The magnetron 130 includes a magnetic pole 132 of a first polarity and a magnetic pole 135 of an opposite polarity to the first. The magnetron 120 can produce magnetic flux outside of the sputtering surface 112 on the lower side of the target 110 as shown in FIG. 1B. A close loop magnetic field track can be formed outside of the sputtering surface 112 for trapping the electrons and thus enhancing the plasma near the sputtering surface 112. More electrons are trapped near the maximum magnetic field produced by the magnetron 130 parallel to the sputtering surface 112. The locations having the maximum magnetic field strength form a close loop that can guide the migration path for the free electrons. The closed-loop magnetic field enhances the ionization efficiency of the sputtering gas and lowers the operating pressure during sputter deposition. The enhanced sputtering due to magnetic field can produce an erosion pattern over the sputtering surface 112 after repeated sputtering operations, as shown in FIG. 1D.
The drawback of the deposition system 100 is that the magnetron 130 is stationary relative to the target 110 during the depositions, which produces non-uniform erosion on the sputtering surface 112 of the target 110. The non-uniform erosion can result in low target utilization and re-deposition of sputtered target materials on the areas of the sputtering surface 112 having low magnetic field strength. Some of the accumulated materials can fall off the target 110 and land undesirable particle deposition on the substrate 115.
Another conventional deposition system 200 is shown in FIGS. 2A and 2B. The deposition system 200 includes a large target 210, a vacuum chamber 220, and a magnetron 230 on the back side (opposite to the sputtering surface 212) of the large target 210. The magnetron 230 can scan across along the direction 250. The substrate 215 is held over a substrate holder 217. The substrate 215 remains stationary during the deposition for target with dimensions larger than the substrate, and can have a relative movement to the target 210 for smaller target.
Although the scanning of the magnetron 230 relative to target 210 can improve the target utilization and prevent target material re-deposition, the deposition system 200 has the disadvantages of using a large and thus expensive target. In addition, the areas of the target 210 at the ends of the scanning direction can only be reached by a single track of the magnetron 230, while the middle section of the target 210 is scanned by both tracks of the magnetron. This limitation lowers the sputter rate near the edges of the target 210 resulting in non-uniform deposition over the substrate 115.
Yet another conventional deposition system 300 is shown in FIG. 3. The deposition system 300 includes a circular target 310, a stationary magnetron 330, a substrate 315 that can be transported along one direction, and a vacuum chamber 320. The circular target 310 can rotate around the magnetron 330 by a rotational mechanism to expose different areas of the circular target 310 the magnetic fields of the magnetron 310 so that the target materials can be sputtered at the sputtering surface 312. The erosion pattern can be more uniform due the circular movement of the target 310. The high cost of the single-piece circular target 312 is a significant disadvantage in the deposition system 300. Moreover, target material is often is sprayed on the backing plate 313, which reduces the quality of the deposition material. The vacuum seal of the rotational transport mechanism is also an engineering challenge. System reliability can be reduced due to unreliable vacuum sealing at the rotational transport mechanism.
Another disadvantage of the conventional deposition systems is that they are not suitable for thick target, especially the ones comprising magnetic or ferromagnetic materials. The magnetic fields produced by the magnetrons cannot penetrate the thick target. The limitation in the target thickness reduces the amount of materials that can be deposited for each target change-over.
Yet another disadvantage of the conventional deposition systems is that the target width has to be large enough to accommodate at least one magnetic field loop. In practice, the target width is typically more than 3 inches wide. This will increase target cost and increase system size.
Yet another disadvantage of the conventional deposition systems is that the deposition is made only on one side of the substrate. A double-sided conventional deposition system 400 requires two opposing magnetrons 430a and 430b and two associated targets 410a and 410b in a vacuum chamber 420 as shown in FIG. 4. There can be two separate substrates 415a and 415b, or two deposition surfaces of a single substrate.